Systems are known in which equipment activation signals are wirelessly transmitted to a receiver which responds thereto by activating the equipment. Such signals are used, for example, to allow remote unlocking or opening of a barrier separating a user from a protected or secure area. The transmitted signals generally include an access or security code which is analyzed by the receiver to identify whether the user causing the signal transmission has permission for access to the protected area.
Frequently, the wireless access signals are transmitted by means of a radio frequency (rf) carrier. In many cases, these systems are used in consumer products which dictate that costs and energy consumption are kept to a minimum. It has been discovered that such communication systems may, from time to time, lose their effectiveness due to interfering rf signal transmission by other more powerful transmitters. For example, a barrier movement operator such as a garage door operator, may transmit relatively low power rf signals including a security code to a barrier controller which responds thereto by selectively moving the barrier. One common frequency for the transmission of such security codes is 390 MHZ. Should a higher power rf transmitter be operating nearby at or nearly at the 390 MHZ frequency the receiver at the barrier movement operator may be overloaded and unable to respond properly to a transmitted security code. As should be apparent, this results in the user being unable to control the barrier with his or her remote security transmitter. Further, when the powerful transmitter operates, the inability to control the barrier may appear as an intermittent problem because sometimes the code transmission controls the barrier and sometimes it does not.
A need exists for a wireless code transmission and reception system which is less prone to interfering signal transmission.